I was sending this to someone who is on ferret genetics but then I
recalled someone here who had a blaze recently have a small and
non-surviving litter who was not thinking in terms of spaying, so I
figured I'd share parts of the post as a reminder of how unfair it is
to breed such individuals:
 
Well, in the first place while ferrets might have Waardensburg, it is
more likely that the neural crest genetics difference which has caused
health problems is one of the others: KIT or a different one.
 
Secondly, it is not known if the cardiac crest problem which can be
seen in accompaniment with some neural crest genetic disorders is
encountered in ferrets.  Sometimes the two go together in mammals but
that is not consistently the case.
 
If you go to the Ferret-Genetics website (at Yahoogroups) and search you
will find posts from a number of people on this sort of topic.  Brett
Middleton (who has said something along the lines of "stick to colors
but skip patterns" (I forget if "skip dilutes" was also in there.), is a
geneticist and has given excellent info, and there are journal articles
with addresses given by others.
 
I recall that the ones on cardiac crest disorders were given by
Rebecca/Wolfy (Wolfysluv) if that helps with the search but they did
not specifically involve ferrets.
 
In other mammals most individuals with cardiac crest disorders do not
survive to be born, or die at birth or shortly after, as I recall from
the articles.
 
Certainly, it is possible to survive such a disorder.   When she is
larger our middle niece's baby is going to have surgery to repair one
type of failure of fetal vessels to shut off which can happen as part
of the complex of cardiac  crest disorders.  (The cause of her's is not
determined.)  Tabitha's is limiting but not dangerous at this stage so
they can wait a bit for her to be stronger and larger.  I doubt many
people would consider or be able to perform major cardiac vessel surgery
for a ferret kit, though.
 
Neural Crest mutations (Waardensburg, KIT, whichever) can involve a
number of limiting factors in ferrets specifically: the individuals have
been reported to more often be poor parents with more infants dying, more
often have still births, more often to die young and possibly develop
common health problems younger, more likely to be deaf, more likely to
have jaw malformations, more likely to have intestinal problems, etc.
Long experience by breeders in the U.S.  show all too often that it is
irresponsible to breed them, so if you know folks who are considering
doing so, please, discourage them strongly.
 
Two of the classic markings of such neural crest variants include a
blaze on the head or a white (or mostly white) head throughout life.
(It is not roaning -- a lightening that can happen with age.)
 
(P.S. Dr. Brett Middleton has also written on this in
http://fhl.sonic-weasel.org)
[Posted in FML issue 4480]